This invention relates to a method and an apparatus for producing extruded ceramic green products, and more particularly to a method and apparatus for producing ceramic honeycomb structures as catalyst carriers.
In order to produce, for example, ceramic honeycomb structures up to the present, after a ceramic material has been mixed and kneaded in a kneader, the kneaded product was extruded in column-shaped bodies in suitable sizes from a vacuum auger machine and the column-shaped bodies were supplied into a plunger molding machine from which the bodies were extruded.
FIG. 1 illustrates in section a vacuum auger machine to be used for the purpose described. The vacuum auger machine includes a vacuum kneading section having a screw-type mill 23 and a vacuum chamber 24 for kneading the ceramic material to obtain ceramic batches for forming the products, a ceramic batch transfer section having an auger 25 for transferring the ceramic batches in the vacuum chamber 24, and a column-shaped green product forming section having a forming column ring 1 for forming the ceramic batch transferred by the auger 25 into column-shaped green products. These sections are located on a frame 27.
The screw-type mill 23 is used for transferring the ceramic material supplied from a ceramic material supply opening 22 into the vacuum chamber 24, while the ceramic material is being kneaded. In the vacuum chamber 24, bubbles and the like in ceramic batches supplied as kneaded batches for forming are removed and the ceramic batches are loosened when falling by gravity and then supplied to the ceramic batch transfer section.
The ceramic batch supplied into the ceramic batch transfer section is transferred while being compressed by the auger. When the ceramic batch is transferred by the auger, it passes through a grid drum 9 to be crushed and loosened so as to remove laminations included in the ceramic batches. Thereafter, the ceramic batch passes through a guide passage 19 of the forming column ring 1, while being formed into a column-shaped green product which is then extruded at an extruding opening 11 as shown by an arrow A in FIG. 1.
The resultant column-shaped green product is cut in predetermined lengths by a cutter (not shown) provided on a side of the outlet of the forming column ring 1. The column-shaped products of the predetermined lengths are then supplied to a plunger molding machine (not shown) preparatory to a next process. In this case, the column-shaped products must have diameters and lengths permitting the products to be inserted into a cylinder of the plunger molding machine. These column-shaped products are then caused to pass through an extruding die of the plunger molding machine, thereby producing honeycomb structures.
The above explained method is so-called "batch process", wherein the column-shaped products extruded from the extruding opening 11 of the vacuum auger machine shown in FIG. 1 have to be loaded one by one into the plunger molding machine for the next process by means of a movable loading machine.
In this case, however during this loading process the column-shaped products stay in a stock yard for a period of time until they are loaded into the plunger molding machine. During such an awaiting period, moisture tends to evaporate from surfaces of the column-shaped products to be locally dried and hardened. Moreover, such a drying may take place until they are extruded from a plunger cylinder of the plunger molding machine in the next process.
The dried outer surfaces of the column-shaped products detrimentally affect resultant products having a predetermined shape obtained through an extruding die by an actuation of a ram head by means of a hydraulic plunger. In more detail, the hardened surfaces make rough outer surfaces of extruded honeycomb structures or the hardened portions of ceramic batch mix with inner material of the formed structures to cause strains therein or forming grooves of a forming die are partially clogged with the hardened ceramic material to cause defects in the extruded honeycomb structures.
In the batch process, moreover, the honeycomb structures extruded from the plunger molding machine are left as extruded until next drying process. In the same manner above described, therefore, the honeycomb structures are partially dried and suffer cracks or uniform construction of the structures can not be obtained in the next drying and firing processes so that strains imperatively remain in the structures. In general, the outer surfaces of the extruded products are considerably dried by frictional heat caused by contact resistance between the ceramic batch and extruding dies.